1. Field of the Invention
The present invention relates to automatic personal protection devices and more particularly to electronic lockout devices to prevent user interference with protection barrier safety devices.
2. Background and Prior Art
Many industrial and consumer machines perform operations such as stamping, cutting, spinning, milling, welding, etc. which present potential dangers to users. An example of such a machine is a spin welder for container sections such as that disclosed in U.S. Pat. No. 3,800,400 to Mistarz et al. wherein a plurality of gears, rotating wheels, spinning shafts, etc are utilized. If loose clothing is caught in such a device or if an operator's hands, eyes, etc. have direct access to the moving equipment while it is in operation, a hazard is created which can result in serious injury. It is therefore common on such equipment to utilize a protective shield or other lockout device to prevent direct access to the dangerous areas of the operating equipment. Such a shield can be in the form of a hinged door which, when closed, effectively blocks operating personnel from deliberately or accidentally interfering with operating equipment. In order to be effective, such door shields are usually provided with some sort of a lockout switch which controls power to the equipment. If the door or shield is not securely closed, the switch will prevent the equipment from operating. Known switches for this purpose can be contact operated switches (e.g. microswitch), magneticly operated switches (e.g. reed switch) or the like and can be normally opened or normally closed depending upon the configuration of the associated circuitry for operating the equipment. Also known are radio-frequency (rf) guards which utilize an rf loop and an antenna. If any capacitance, such as an operator's hand, is positioned between the loop and the antenna, it will be sensed by the antenna which will shut down the equipment.
In connection with such safety shield and electrical interlocks, problems may arise if the operator of the equipment deliberately attempts to defeat the electrical interlock. For example, should the electrical interlock switch malfunction or become misaligned with its closure member, maintenance personnel may attempt to remedy the problem by positioning a magnet near the switch (if it is magnetically activated) or by simply "jumping" any contact operated switch. RF switches can be similarly defeated. Similar measures can also be taken if the operator, for any reason, deliberately attempts to operate the equipment without the safety system provided. Thus, one of the major problems with prior art safety systems is the relative ease with which it can be defeated by operator personnel.